1. Field of the Invention
The invention relates to a circuit arrangement with a first input connection and a second input connection, with a first output connection and a second output connection, with a supply voltage connection as well as with a voltage-controlled voltage source, an output stage and a short-circuit protective circuit, whereby the output signal from an input voltage applied to the input connections is generated via the voltage-controlled voltage source and the output stage.
2. Description of Related Art
Circuit arrangements of the type being discussed here have been known for a long time in various embodiments and are used universally in circuit engineering, where an input voltage is to be converted into an output signal, whereby the circuit arrangement normally can have available a higher power on the output side than the power that is necessary on the input side to control the circuit arrangement. Such circuit arrangements are typically found in, e.g., isolation amplifiers, signal converters and power modules. A more common application for such circuits is in, for example, the conversion of a voltage of a first voltage range into a voltage of a second voltage range for adapting the first voltage to a standardized voltage interface, which operates with, e.g., voltage values in the range of 0 V to 10 V.
In principle, in the design of circuit arrangements of the type being discussed here, operating safety, but also certifiability under relevant standards, should be considered for the sake of practical handling, as the circuit behaves in the case of an output-side short circuit, i.e., if the output connections are connected to one another in a very low-ohmic manner. If no special circuit-engineering measures are taken, the danger exists in the case of short circuiting that the output-side behavior of the circuit arrangement can no longer be controlled on the input side, a high loss of power is converted in the circuit arrangement or the output stage of the circuit arrangement, and electrical devices connected to the circuit arrangement and/or on the output side are even destroyed.
For these reasons, circuit arrangements of the type at issue here are often provided, on the output side, with electronic current limiters that, in the case of a short circuit, at least prevent destruction of the circuit arrangement. If the output stage is controlled, for example, via current driven by the voltage-controlled voltage source, it is known from experience and relevant literature to measure the load or short-circuit current flowing via the—short-circuited—output connections and to direct the current controlling the output stage based on the level of the load current to an equal extent past the output stage. Such a short circuit protective circuit can be implemented by, for example, a bipolar transistor, which is controlled as a function of the voltage decreasing on a “sensor” resistor arranged in a load circuit and which directs the current controlling the output stage to the input of the output stage and thus prevents a further increase of the load current and thus limits the short-circuit current (Tietze, U.; Schenk, Ch.: “Halbleiter-Schaltungstechnik [Semiconductor Circuit Engineering],” 12th Edition, Springer-Verlag, 2002, pages 909-910).
It is disadvantageous in such short-circuit protective circuits, which detect the level of the load current via a “sensor” resistor in the load current path and ultimately also the short-circuit current, that the load current-dependent drop in voltage influences the output signal via this resistor—thus, for example, a voltage that is applied to the output connections, in normal operation—and causes a constant power loss. It is also disadvantageous when, using simple, unregulated semiconductor components, such as, e.g., bipolar transistors in the short-circuit protective circuit, that the level of the short-circuit current that triggers the protective circuit is temperature-dependent based on the temperature dependency of the semiconductor components. In the case of the above-mentioned bipolar transistors, this is, e.g., the temperature dependency of the flow voltage of the diodes, operated in the forward direction, within the bipolar transistors. When using a bipolar silicon transistor controlled via the base-emitter segment, the temperature dependency of the flow voltage of the base-emitter diode is, for example, −2 mV/K.
The problem underlying the teaching of this invention is therefore to configure and to develop a circuit arrangement with a voltage-controlled voltage source, with an output stage and with a short-circuit protective circuit such that the above-mentioned drawbacks, especially the temperature dependency of the short-circuit current and/or the influence of the output signal by the load current are—at least partially—avoided.